Extremist bomb attacks killed 126 people in one of Pakistan's deadliest days for years, raising concerns on Friday about rising violence in the nuclear-armed country ahead of general elections.

Two suicide bombers killed 92 people and wounded 121 after they targeted a crowded
snooker club in the southwestern city of Quetta on Thursday, in an area dominated by Shiite Muslims from the Hazara ethnic minority.

Extremist Sunni militant group Lashkar-e-Jhangvi claimed responsibility for what was the worst ever sectarian attack on Shiites, who account for around 20 percent of Pakistan's 180 million population.

Hundreds of Shiites staged a sit-in at the devastated snooker hall on Friday, refusing to bury loved ones until the army takes responsibility for security in Quetta from paramilitary and police officers.

The government in Baluchistan province, which is also fighting a separatist insurgency, announced three days of mourning, but the protesters squatted on the road alongside around 30 bodies draped in shrouds and placed in coffins.

It was the deadliest attack in Pakistan since suicide bombers killed 98 people outside a police training centre in the northwest in 2011 -- an attack claimed by the Pakistani Taliban.

Meanwhile, unidentified men fired rockets on NATO containers carrying goods for international troops operating in Afghanistan, killing one person and destroying at least five vehicles in the Hazar Ganji area on the outskirts of Quetta on Friday.

"A group of at least 12 unidentified men attacked the terminal and fired rockets, which triggered a massive fire and gutted five out of

He said that the attackers escaped after also shooting dead an employee at a nearby petrol pump.

People search for their relatives' belongings at the site of the bomb blast in Quetta. (Reuters)

A local police official Noor Bukhsh Mengal also confirmed the incident.

Earlier Thursday, a bomb detonated under a security force vehicle in a crowded part of Quetta, killing 11 people and wounding dozens.

A bomb at a religious gathering in the northwestern Swat valley killed 22 people and wounded more than 80, the deadliest incident in the district since the army in 2009 fought off a two-year Taliban insurgency.

US state department spokeswoman Victoria Nuland said on Friday, "We join Ambassador Richard Olson in offering the families of those killed in these brutal attacks in Quetta, in Swat, in Karachi, more than a hundred people dead over the last 24 hours -- we offer those families our deepest condolences and wish the injured a speedy recovery.

"We obviously stand with the people of Pakistan in strongly condemning these senseless and inhumane acts. And more broadly, we remain concerned about extremist violence of any kind in Pakistan and remain committed to working with the government of Pakistan to combat terror."

At the snooker club, the first bomber struck inside the building then, 10 minutes later, an attacker in a car blew himself up as police, media workers and rescue teams rushed to the site, said police officer Mir Zubair Mehmood.

"The death toll is now 92," said police official Hamid Shakeel.

Lashkar-e-Jhangvi claimed responsibility in telephone calls to local journalists. The group has links to Al-Qaeda and the Taliban, and was involved in the kidnap and beheading of reporter Daniel Pearl in January 2002.

The attacks, coupled with violence in the northwest, revived warnings from analysts that Islamist militancy could threaten national elections, expected sometime in May.

Polls would mark the first time an elected civilian government in Pakistan, for decades ruled by the military, completes a term in office and is replaced by another democratically elected government.

The Human Rights Commission of Pakistan demanded that the government take immediate steps to clamp down on "murdering mayhem" ahead of the elections.